Cobalt Nanoclusters Research Articles

Hydrogenation and Tandem Reactions of Nitroarenes on N-Doped Carbon−Coated Cobalt Nanoclusters

Hydrogenation and Tandem Reactions of Nitroarenes on N-Doped Carbon−Coated Cobalt Nanoclusters

Structure Types and Magnetic Behavior of Cobalt Nanoclusters.

Caprylic hydrazide ligands are ideal ligands for the synthesis of novel polynuclear metal complexes, because they contain many N,O coordination atoms with a strong coordination ability, abundant hydrogen-bond donors, acceptors, and large conjugation systems. Here, we successfully obtained one dodecanuclear cobalt nanocluster [CoII8CoIII4(L1)4(Py)12(CH3OH)4(CH3COO)4]·(CH3OH)13 (1) and one octadecanuclear cobalt nanocluster [CoII18(L2)6(Py)48]·(DMF)5·(CH3OH)8 (2) by using H6L1 and H6L2 ligands, respectively (Py = pyridine; DMF = dimethylformamide). The cyclic cobalt nanocluster 1 can be regarded as two pentanuclear cobalt units (Co5(N-N)4) connected by two cobalt ions, and it is a mixed-valent Co nanocluster. Every H6L1 ligand contains 10 coordination atoms, each of which coordinates with the Co ions. And every two H6L1 ligands form a structure similar to a handshake. The abnormal cylindrical cobalt nanocluster 2 can be regarded six trinuclear cobalt units Co3(N-N)2 connected by one L26- ligand, and every L26- ligand splits the structure on both sides, with a twisted cyclohexane in the middle. AC magnetic susceptibilities show that nanocluster 1 exhibits no frequency-dependent behavior, but nanocluster 2 shows an obviously single-molecule magnetic behavior, and the relaxation process of the energy barrier is 20.4 K.

Layered double hydroxide supported cobalt nanocluster: size control and the effect in catalytic hydrogen generation

Synthesizing metal nanoclusters with diameters smaller than 5nm is challenging, but desirable because of the high ratio of surface area to interior atom. However, in this report it was achieved by utilizing magnesium-aluminium layered double hydroxide (Mg/Al-LDH) as a host for cobalt citrate anion precursor, which was later reduced into cobalt nanoclusters (Co-NC). Size of the Co-NC was controlled by changing the concentration of cobalt-citrate (Co-citrate) precursor during anion exchange. XRD and FTIR showed that Co-citrate precursor was successfully intercalated on the LDH while nitrogen adsorption/desorption isotherms confirmed that mesopores in the sample were formed after chemical reduction. Furthermore, TEM/STEM observations confirmed the formation of Co-NC. It was also verified that reducing the concentration of Co-citrate from 4mM to 0.5mM resulted in a reduction in the size of Co-NC from 4.4 to 1.3 nm. However, catalytic hydrogen generation from sodium borohydride (NaBH4) hydrolysis experiment indicated that catalytic activity decreased as the size of Co-NC decreases. This is mainly attributed to the limitation in mass transport within the interlamellar space of the smaller cluster LDH compared to the bigger one. Overall, Co-NC-LDH is a promising catalyst for NaBH4 hydrolysis. However, an optimum Co-NC size is critical for enhanced catalytic activity.

Cobalt nanoclusters coated with N-doped carbon for chemoselective nitroarene hydrogenation and tandem reactions in water

Subnanometric cobalt nanoclusters covered by N-doped carbon layers (Co@NC-800) catalyze the chemoselective reduction of nitroarenes and the one-pot synthesis of secondary aryl amines and isoindolinones in aquo media under mild reaction conditions.

Fabrication of Polymer Magnetic Nanocomposites Containing Carbon Nanoparticles Doped with Cobalt Nanoclusters and Study Their Conductivity, Self-Healing and Adhesion Properties

The technology of fabrication of polymer nanocomposites on basis of carbon nanoparticles doped with cobalt clusters, synthesized by original Chemical Vapore Deposition (CVD) technology developed by authors, was elaborated. Carbon shells provide both the protection of ferromagnetic impurities from aggressive environment and new unique properties to the hybride nanostructures. The self-assembling of magnetic clusters coated by carbon shells presents just such example which could be used in the contemporary materials, for example, in strong magnets, analytic instruments (nuclear magnetic resonance tomographs) and nanosensors. Their good conductivity, self-healing and adhesion properties were demonstrated by applying the combined action of temperature, pressure, steady and alternating magnetic fields to stimulate diffusion of magnetic nanoparticles in direction to defect sites. Due to these properties fabricated magnetic polymer nanocomposites could have perspective for potential.

Magnetic Dodecahedral CoC-Decorated Reduced Graphene Oxide as Excellent Electromagnetic Wave Absorber

A two-step method has been adopted to synthesize cobalt nanoclusters in carbon (CoC)-decorated reduced graphene oxide (rGO) from graphene oxide (GO) and ZIF-67 as an excellent stable electromagnetic wave (EMW) absorber. Firstly, the electrostatic force between GO and Co2+ gave rise to in situ growth of ZIF-67 on GO (ZIF-67–GO). Then CoC–rGO was obtained by calcination of ZIF-67–GO hybrids. The ligand is introduced as the nitrogen source to GO. The crystal structure, chemical composition, and magnetic properties of CoC–rGO were investigated by x-ray powder diffraction analysis, Fourier-transform infrared (FT-IR) spectroscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, and vibrating-sample magnetometry. The morphology was observed by scanning electron microscopy and transmission electron microscopy. By adjusting the ratio of GO to ZIF-67, the electromagnetic parameters of CoC–rGO can be optimized. It was found that the sample consisting of 10 wt.% CoC–rGO-2 in a paraffin matrix exhibited excellent EMW absorption performance, reaching a minimum reflection loss (RLmin) of −44.77 dB with thickness of 2.1 mm and an effective bandwidth (RL ≤ −10 dB) of up to 5.2 GHz at thickness of 1.8 mm. The results of this study open an effective and simple avenue for the design of EMW absorbers using metal–organic framework (MOF) and low-cost carbon materials.

In Situ Electron Diffraction Investigation of Solid State Synthesis of Co-In2O3 Ferromagnetic Nanocomposite Thin Films

In situ electron diffraction was used to study structural transformations during the formation of Co-In2O3 ferromagnetic nanocomposite thin films in a thermite reaction of In/Co3O4 bilayer thin films. Heating was performed from room temperature to 600°C at a rate of 4°C/min, while simultaneously electron diffraction patterns were recorded at a speed of 4 frames/min. This made it possible to determine the initiation, 185°C, and finishing, 550°C, temperatures of the solid-state synthesis, as well as the change in the phase composition during the thermite reaction. The synthesized Co-In2O3 film nanocomposite contained ferromagnetic cobalt nanoclusters surrounded by an In2O3 layer, with an average size of 20 nm, and had a magnetization of 400 emu/cm3 and a coercivity of 50 Oe at room temperature. The estimate of the effective interdiffusion coefficient of the reaction suggests that the main mechanism for the formation of the Co-In2O3 nanocomposite is diffusion along the grain boundaries and dislocations.

In situ formed Co clusters in selective oxidation of α-C[sbnd]H bond: Stabilizing effect from reactants

Aerobic oxidation of α-CH bond of organic compounds to valuable chemicals is widely investigated in both fundamental research and industry. Due to the good stability of molecular oxygen, severe reaction conditions are generally required. Herein, by in situ synthesis we used molecular oxygen to induce cobalt nanoclusters with the sensitive catalysis in mild selective oxidation. The cobalt containing clusters with an average diameter around 0.9 nm are in situ prepared in the presence of cis-cyclooctene epoxidation and cyclooctene dimer oxide is formed at the interface to stabilize Co clusters with electron donation as an oil-soluble surfactant. The soluble clusters exhibit high activity in selective oxidation of α-CH bond of ethylbenzene into acetophenone and turnover number (TON) reaches about 7 × 104 during 50 h’ reaction at 373 K, which is around 960 times more active than the one using CoCl2 salt as the catalyst, resulting from efficient mass transportation, π bond interaction and oxygen gas activation. Extended work based on this understanding demonstrates that cobalt nanoclusters also effectively catalyze aerobic oxidation of cyclohexene.

In situ incorporation of cobalt nanoclusters and nitrogen into the carbon matrix: a bifunctional catalyst for the oxygen depolarized cathode and chlorine evolution in HCl electrolysis

The co-insertion of both cobalt and nitrogen into the carbon matrix was achieved from single precursor without any templates. The obtained Co-NSC catalyst was explored bifunctionally towards both oxygen depolarized cathode and chlorine evolution under HCl electrolysis conditions.

Co–In2O3 Nanocomposite Films: Synthesis and Structural and Magnetic Properties

The structural and magnetic properties of granular Co–In2O3 nanocomposite films formed by vacuum annealing of In/Co3O4 film bilayers at a temperature of 550°C have been investigated. The synthesized Co–In2O3 films contain ferromagnetic cobalt nanoclusters with an average size of 60 nm and a magnetization of ~340 emu/cm3 surrounded by the In2O3 layer and exhibit the thermally activated conductivity.

Ethyne-Reducing Metal–Organic Frameworks to Control Fabrications of Core/shell Nanoparticles as Catalysts

An approach using cobalt metal–organic frameworks (Co–MOF) as precursors is established for the fabrication of cobalt nanoparticles in porous carbon shells (core/shell Co@C). Chemical vapor deposition of ethyne is used for controlling the reduction of cobalt nanoclusters in the MOF and the spontaneous formation of the porous carbon shells. The metallic cobalt cores formed are up to 4–6 nm with the crystal phase varying between hexagonally close-packed (hcp) and face-center-packed (fcc). The porous carbon shells change from amorphous to graphene with the ethyne deposition temperature increasing from 400 to 600 °C. The core/shell Co@C nanoparticles exhibit high catalytic activity in selectively converting syngas (CTY 254.1–312.1 μmolCO gCo–1 s–1) into hydrocarbons (4.0–5.2 gHC g-cat–1 h–1) at 260 °C and 3.0 MPa. In addition to the crystal size and phase, the coordination numbers of the cobalt to oxygen and to other cobalt atoms on the surface of the cobalt nanoparticles and the permeability of the porous ca...

Template Assisted Nucleation of Cobalt and Gold Nano-clusters on an Ultrathin Iron Oxide Film

Being the basic building blocks for nano-magnetic and nano-catalytic devices, regular arrays of nano-clusters play a crucial role in modern nanotechnology. One of the possible fabrication methods of periodic nanostructures consists in exploiting nano-patterned substrates as templates for the self-assembly of the deposited atoms. Here, we have investigated the templating properties of a Moire superlattice formed at the interface between a FeO(111)-like ultrathin film and a Ni/Fe(001) substrate. Co and Au, representative of elements with high and low oxygen affinity, respectively, have been deposited on the iron oxide film. Scanning tunneling microscopy reveals that Co nucleates preferentially along the corrugated regions of the Moire superstructure, forming stripes with high aspect ratio. On the other hand, Au atoms nucleate randomly distributed three-dimensional islands on the FeO(111) surface.

Ligand mediated evolution of size dependent magnetism in cobalt nanoclusters.

We use density functional theory to model the impact of a ligand shell on the magnetic properties of CoN (15 ≤ N ≤ 55) nanoclusters. We study three different ligand shells on each nanocluster core size, each known to have different electronic interactions with the surface: pure Cl ligand shells (X-type), pure PH3 ligand shells (L-type), and two component ligand shells with mixtures of Cl and PH3 ligands. The simulations show that the identity, arrangement, and total coverage of the ligand shell controls the distribution of local magnetic moments across the CoN core. On the surface of an unpassivated CoN nanocluster, the Co-Co coordination number (CN) is known to determine the local magnetic moments. Upon the introduction of a ligand, the Co-Co CN remains important, however the nature of the metal-ligand bond changes the extent to which increasing Co-Co CN quenches magnetism. Further, we identify an additional and significant long-range impact on local magnetic moments (LMM) from the PH3 ligand shells. Thus, we establish important design principles of magnetic nanoclusters, where ligand shell chemistry mediates the distribution of LMMs across a CoNLM nanocluster, allowing a route to rational design of specific magnetic properties.

Нанокомпозитные пленки Co-In-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-: синтез, структурные и магнитные свойства

AbstractThe structural and magnetic properties of granular Co–In_2O_3 nanocomposite films formed by vacuum annealing of In/Co_3O_4 film bilayers at a temperature of 550°C have been investigated. The synthesized Co–In_2O_3 films contain ferromagnetic cobalt nanoclusters with an average size of 60 nm and a magnetization of ~340 emu/cm^3 surrounded by the In_2O_3 layer and exhibit the thermally activated conductivity.

Synthesis and antibacterial effects of cobalt–cellulose magnetic nanocomposites

Green synthesis is employed to prepare cobalt/cellulose nanocomposites with antibacterial and magnetic properties. The cellulose-stabilised, cubic (α-cobalt) cobalt nanoclusters are distributed evenly over the surface of the cellulose fibres.

Morphology-controlled synthesis of cobalt nanostructures by facile electrodeposition: transition from hexagonal nanoplatelets to nanoflakes

Cobalt hexagonal nanoplatelets and cobalt nanoflakes were produced by electrodeposition onto aluminium from cobalt sulphate solutions. The dependence of the nanostructure morphology on cobalt ion concentration and potential was investigated under potentiostatic and pulsed-electrodeposition. Under potentiostatic electrodeposition, cobalt hexagonal nanoplatelets were obtained with cobalt ion concentration equal to 0.01 and 0.1M, while cobalt hydroxide nanoflakes were formed as the cobalt ion concentration was increased to 0.2M. Under pulsed electrodeposition, both hexagonal nanoplatelets and hydroxide nanoflakes could be obtained with cobalt ion concentration equal to 0.1M by modulation of the imposed current/potential wave. The analysis of the current transients recorded under potentiostatic electrodeposition and the microscopic analysis of the deposits indicate that three-dimensional diffusion control cannot adequately describe the growth of the cobalt nanostructures. We propose that an aggregative growth mechanism involving the formation and the surface diffusion of cobalt nanoclusters can explain the influence of electrodeposition parameters on the morphology of the cobalt nanostructures.

Optical studies of cobalt implanted rutile TiO2 (110) surfaces

Present study investigates the photoabsorption properties of single crystal rutile TiO2 (110) surfaces after they have been implanted with low fluences of cobalt ions. The surfaces, after implantation, demonstrate fabrication of nanostructures and anisotropic nano-ripple patterns. Creation of oxygen vacancies (Ti3+ states), development of cobalt nano-clusters as well as band gap modifications have also been observed. Results presented here demonstrate that fabrication of self organized nanostructures, upon implantation, along with the development of oxygen vacancies and ligand field transitions of cobalt ion promote the enhancement of photo-absorbance in both UV (∼2 times) and visible (∼5 times) regimes. These investigations on nanostructured TiO2 surfaces can be important for photo-catalysis.

Cobalt nanoparticles as recyclable catalyst for aerobic oxidation of alcohols in liquid phase

Cobalt nanoparticles prepared at room temperature from cobalt sulphate and tetrabutyl ammonium bromide as surfactant have been found to be effective oxidation catalysts. Palladium and platinum nanoparticles (average size 4–6 nm) can also be prepared from PdCl2 and K2PtCl4, respectively, using the same surfactant but require high temperature (~120 °C) and much longer preparation time. Agglomeration of nanoparticles prepared from metals like palladium and platinum in common solvents, however, restricts their use as catalysts. It is therefore our endeavour to find the right combination of catalyst and solvent that will be beneficial from industrial point of view. Magnetic property measurement of cobalt nanoclusters was made using SQUID to identify their reusability nature. Herein, we report the use of cobalt nanoparticles (average size 90–95 nm) in dichloromethane solvent as effective reusable catalysts for aerobic oxidation of a variety of alcohols.

Effect of Cobalt Concentration and Oxygen Vacancy on Magnetism of Co Doped ZnO Nanorods.

Zn(1-x)Co(x)O (x = 0-0.07) single-crystalline nanorods were prepared by a modified microemulsion route. The crystalline structure, morphology, optical, and hysteresis loop at low and room temperature of as-prepared materials were characterized by XRD, TEM, PL spectra, and magnetic measurement respectively. The nanorods are 80-250 nm in diameter and about 3 μm in length. X-ray diffraction data, TEM images confirm that the materials synthesized in optimal conditions are ZnO:Co single crystalline solid solution without any impurities related to Co. The PL spectra show that the ferromagnetic samples exhibit strong Zn interstitials and oxygen vacancy emission indicating defects may stabilize ferromagnetic order in the obtained diluted magnetic semiconductors. Magnetic measurements show that the Zn(1-x)Co(x)O nanorods exist obvious ferromagnetic characteristics with T(c) above 300 K. M(s) and coercivities first increase and then decrease with dopant concentration increasing, reaching the highest for 3% doping level. The structural and magnetic properties of these samples support the hypothesis that the FM of DMS nanorods is due to a defect mediated mechanism instead of cobalt nanoclusters and carrier mediated.

Nitrogen Activation in a Mars–van Krevelen Mechanism for Ammonia Synthesis on Co3Mo3N

Co3Mo3N is one of the most active catalysts for ammonia synthesis; however, little is known about the atomistic details of N2 adsorption and activation. Here we examine whether N2 can adsorb and activate at nitrogen surface vacancies. We have identified the most favorable sites for surface nitrogen vacancy formation and have calculated vacancy formation free energies (and concentrations) taking into account vacancy configurational entropy and the entropy of N2 at temperature and pressure conditions relevant to ammonia synthesis (380–550 °C, 100 atm) via a semiempirical approach. We show that 3-fold hollow bound nitrogen-containing (111)-surfaces have surprisingly high concentrations (1.6 × 1016 to 3.7 × 1016 cm–2) of nitrogen vacancies in the temperature range for ammonia synthesis. It is shown that these vacancy sites can adsorb and activate N2 demonstrating the potential of a Mars–van Krevelen type mechanism on Co3Mo3N. The catalytically active surface is one where 3f-hollow-nitrogens are bound to the molybdenum framework with a hexagonal array of embedded Co8 cobalt nanoclusters. We find that the vacancy-formation energy (VFE) combined with the adsorption energy can be used as a descriptor in the screening of materials that activate doubly and triply bonded molecules that are bound end-on at surface vacancies.